During percutaneous surgery on the spinal column, in particular percutaneous spinal stabilization surgeries, several pedicle screws are screwed in several vertebral bodies in most cases, and then the pedicle screws are connected with each other by means of a connecting or stabilization bar in such a way that the stabilization rod fixes the vertebral bodies in a desired position in relation to each other.
In most cases, the pedicle screws used for such a vertebral reposition have a screw head in the shape of a tulip, a so-called tulip head. Furthermore, the pedicle screws have in most cases elongated flanks which extend from the tulip head in the longitudinal direction of the pedicle screw and block off the instrument access to the tulip head from the surrounding tissue. After the successful placement of the implant, the elongated flanks are removed from the pedicle screws.
As an alternative to pedicle screws with elongated flanks, pedicle screws with flanks of a regular length in combination with pipe-shaped attachments, so-called downtubes, can be used as well. Here, one downtube each is placed on the tulip head of one pedicle screw each and/or is connected with the pedicle screw/coupled with it in a detachable manner and also serves to block off the instrument access to the tulip head from the surrounding tissue.
After the pedicle screws have been screwed in the respective vertebral bodies, the stabilization bar is threaded through entrance openings between the elongated flanks and/or in the downtube of each pedicle screw in the tulip head of each of the pedicle screws, with the downtube connected and/or with elongated flanks connected with the pedicle screw.
After the stabilization bar has been threaded in and placed in the tulip heads of all desired pedicle screws, the stabilization bar is fixed in each pedicle screw by means of a set screw. The set screw is screwed in each tulip head of each pedicle screw through the instrument access kept open by the elongated flanks and/or the downtube.
In practice, the threading in of the stabilization bar in the tulip heads of the pedicle screws is extremely difficult because the operating physician/surgeon cannot see the entrance openings between the elongated flanks and/or the entrance openings in the downtube of a respective pedicle screw. As a result, the operating physician/surgeon has to blindly guess where the entrance opening of each pedicle screw is from the entrance opening of the stabilization bar in the body and try to hit it. It is particularly challenging to thread in the stabilization bar when the stabilization bar is relatively long and/or when relatively many pedicle screws have to be connected with each other. This is aggravated by the fact that the pedicle screws often are offset relative to each other because of different screw-in angles and are therefore not aligned with each other.
For this reason, the operating physician/surgeon tries in most cases to deduce the position of the distal end of the stabilization bar from his point of view from the position and alignment of the bar insertion device used to move and introduce the stabilization bar. Here, the bar insertion device is an instrument with which the operating physician/surgeon grasps and moves the stabilization bar during the threading-in process.
First, the operating physician/surgeon introduces the stabilization bar in the patient's body and tries to navigate it towards a first pedicle screw. When the downtube of the pedicle screw and/or the elongated flanks of it start(s) to move, this movement indicates to the operating physician/surgeon that the distal end of the stabilization bar is close to the pedicle screw and/or rests on it. As soon as the downtube and/or the elongated flanks start(s) to move, the operating physician/surgeon tries to thread in and/or slide in the stabilization bar. Due to the above-mentioned offset between the pedicle screws, however, the stabilization bar may also be slid past the downtube and/or the elongated flanks of the pedicle screw on the outside.
A check of the correct positioning of the stabilization bar during or also after surgery by means of radiography is not possible because with radiographs taken in the anterior-posterior direction, the downtubes and/or the screw heads of the pedicle screws block the beam path. Even with radiographs taken in the lateral direction, the position of the stabilization bar can be determined only insufficiently because the position of the stabilization bar can be detected, but not whether it is also in the right spatial depth, i.e. in or next to the downtube and/or between or next to the elongated flanks of each pedicle screw. So the operating physician/surgeon gets no feedback and so is not able to check either whether the stabilization bar is in the downtube and/or between the elongated flanks of a selected pedicle screw.
In practice, the operating physician/surgeon tries to make do in most cases with introducing a screwdriver shaft in the instrument access defined by the downtube and/or the elongated flanks of a pedicle screw and then jiggles the bar insertion device connected with the stabilization bar. When the screwdriver shaft moves, this indicates the stabilization bar is in the downtube and/or between the elongated flanks. However, this procedure only allows for a very imprecise and relatively error-prone registration of the presence or absence of the stabilization bar in the tulip head of the pedicle screw.
Another possible solution would be to equip the tulip head of the pedicle screw and/or the end of the downtube facing the pedicle screw with a lamp which enables the operating physician/surgeon to perform a direct visual check of the positioning of the stabilization bar, but the costs of a such a system would not be acceptable from a financial point of view.
In summary, it has to be noted therefore that the insertion of the stabilization bar in the tulip heads of the pedicle screws is usually accomplished based on the trial-and-error method. This very imprecise and time-consuming procedure increases the stress on the patient caused by the surgery because of extended anaesthesia times as well as the price of the surgery.